Andrew Peace. 1. 2. 3. 4 ..... Robin Sturdy, Phil Ratcliffe, Bill Mason, Graham. Pyatt, Simon Hodge ... Ferris-Kaan, R., Humphrey, J.W. and Peace, A.J.. (1998).
Biodiversity in Planted Forests by Jonathan Humphrey, Richard Ferris, Martin Jukes and Andrew Peace
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Overmature Sitka spruce: a natural reserve to encourage structural diversity and deadwood habitats
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Long-tailed tit nesting in gorse within a forest ride
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Chickweed wintergreen, a characteristic herb of northern forests
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Hoverflies feeding on leopard’s bane
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Introduction
structure, and the occurrence of particular tree
The majority of planted forests in Great Britain were
link between such indicators and wider biodiversity
established in the 20th century, usually on previously
has not been substantiated to the same degree in
open ground with no recent history of forest cover
British forests as in other countries.
(Hodge et al., 1998), but occasionally through
In this article we present results from a 5-year
conversion of ancient semi-natural woodland
programme of research aimed at:
(Spencer and Kirby, 1992). Introduced conifer species such as Sitka spruce (Picea sitchensis) and Corsican pine (Pinus contorta var. maritima) make up a large proportion (66%) of the planted area. Opinions differ as to the potential value of these ‘new forests’ for biodiversity. Attention has often been drawn to deleterious effects on the flora and fauna of the habitats which forestry replaces or modifies (e.g. Ratcliffe and Thompson, 1989), but there have also been a number of studies which
species such as birch (Betula spp.). However, the
1. Obtaining baseline information on the types/levels of biodiversity in planted forests. 2. Evaluating the contribution of planted forests to the conservation of native flora and fauna through comparisons with semi-natural woodlands. 3. Identifying potential biodiversity indicators by relating the diversity of range of measured taxa to soil, climate, vegetation and stand structure variables.
have highlighted the positive value of planted forests
Summary data are presented for all taxa analysed to
for wildlife (e.g. Petty et al., 1995). However, these
date. Initial results from this programme were
studies have been mostly site specific, and there
presented in Forest Research Annual Report
have been no comparative studies of plantations of
1997–1998 (Ferris-Kaan et al., 1998). Ground
different crop species in contrasting bioclimatic
vegetation, fungi, lichen, bryophyte and selected
zones, or on a range of varied site types. Similarly,
invertebrate datasets are considered in more detail,
there have been few attempts to compare the
and potential indicators of diversity within these
biodiversity of planted forests with that of native or
groups are discussed. A number of management
semi-natural woodlands. With continuing pressures
options for improving habitat quality are identified.
on forest managers to improve the biodiversity of
A full analysis of the datasets for these and other
planted forests, e.g. the Forest Certification process
species groups are presented in a forthcoming
(Anon., 2000), baseline information is urgently
Technical Paper based on the proceedings of a
needed to provide a quantitative framework for
symposium held at Harrogate in November 2000
understanding the levels and types of biodiversity
(Ferris and Humphrey, in press).
currently found in plantations, and to inform the development of biodiversity enhancement strategies.
Study sites
An additional problem is that the comprehensive
Assessment sites were selected from within the
assessment of biodiversity is an extremely difficult
‘lowland’, ‘foothill’ and ‘upland’ bioclimatic zones of
task. It is rarely cost-effective or practical to
the Ecological Site Classification system (ESC; Pyatt
conduct a complete census of all taxa within a forest
and Suárez, 1997). The zones are defined by annual
stand, let alone an entire catchment or forest
precipitation totals (lowlands < 800 mm; foothills
landscape. Therefore, the identity of biodiversity
800–1500 mm; uplands >1500 mm). Study sites
‘indicators’ or surrogate measures of biodiversity
were established in the main crop and semi-natural
has become a research priority in recent years
woodland types within each zone (Figure 1). At the
(Ferris and Humphrey, 1999). Examples of potential
majority of sites, a chronosequence of four 1 ha
indicators include: deadwood, vertical stand
(100 m x 100 m) permanent sample plots was
26
established in forest stands encompassing different
Practicality and cost also influenced the selection of
growth stages based on the normal economic
species groups to assess. Invertebrates were
rotation (1: pre-thicket, 2: mid-rotation, 3: mature, 4:
sampled from deadwood and three separate vertical
overmature). Wherever possible, individual
strata (canopy, sub-canopy, ground). Canopy
chronosequences were established on sites with
dwelling species were sampled using a canopy
similar soils, climate and site history.
insecticide fogging technique (Jukes et al., in press), sub-canopy species by malaise traps (Humphrey et al., 1999), and ground species by pitfall traps (Jukes et al., 2001). The frequency and abundance of
Key
Glen Affric Queens Clunes Beasdale Knapdale Taynish Glentress Kielder
Sitka spruce - uplands Sitka spruce - foothills
vascular plants and fungi were sampled in eight sub-
Oak - uplands Oak - lowlands
plots within each 1 ha plot (Ferris and Humphrey, in
Scots pine - foothills Scots pine - lowlands
press). Species frequency and abundance estimates
Corsican pine - lowlands Norway spruce - lowlands
were made for lichens and bryophytes growing on individual pieces of deadwood (Humphrey et al., in press). Volume and decay status of fallen deadwood (logs), standing deadwood (snags) and
Sherwood Fineshade
stumps were recorded within each plot. Songbird
Thetford
monitoring was undertaken by point counts and
Dean
territory mapping (Ferris and Humphrey, in press).
Windsor
F I G U R E
Alice Holt
Data analysis methods for the various groups are
New Forest
described in full in the publications cited above.
1
Location of biodiversity assessment plots; 52 plots were sampled in total over a 4-year period.
Overview of results Over 2000 species have been recorded to date (Table 1) with nearly half of these being invertebrates. A surprisingly high number of species were recorded in the planted stands, with lowland Scots pine and Norway spruce stands being the
Assessment methods
most species-rich of all the crop types. Stands in northern Britain (foothills and upland) had generally
Plots were selected to minimise heterogeneity in
less diverse invertebrate and songbird communities
stand structure, species composition, topography
than those in the south, but richer lichen and
and hydrology. A standardised system of
bryophyte communities. It had been expected that
assessment was established to maximise potential
the native woodland stands would be considerably
comparisons between measured attributes and to
more species-rich than the plantations, but this was
minimise disturbance during sampling. The plots
only the case for some groups such as vascular
were permanently marked. Assessments were
plants and lichens. These results are due in part to
carried out over a 3–4 year period and covered:
under-sampling of some groups in the native stands
structural aspects of biodiversity, such as vertical
(e.g. birds, Table 1), and to a lower number of stands
foliage cover and deadwood; taxa important in
surveyed (e.g. 4 upland oak stands compared to 8
ecosystem functioning (e.g. fungi); a range of
upland Sitka spruce stands). However, the positive
different groups making up the ‘compositional’
value of plantations for groups such as the beetles
aspect of biodiversity (e.g. invertebrates).
and hoverflies is substantiated by other studies in
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Table 1 Total number of invertebrate, fungi, lichen, bryophyte, vascular plant and songbird species recorded in each forest/climate zone type. Ninety-four coleoptera species (from a total of 474 species records excluding carabids) were recorded in more than one of the three vertical strata (canopy, sub-canopy, ground). Lowland Corsican pine
Scots Norway pine spruce
Foothill Oak
Scots Sitka pine spruce
Upland Sitka spruce
Oak
Total species
Red Data species
Canopy invertebrates Coleopteraa
71
81
86
66
53
66
47
31
225
2
Sub-canopy invertebrates Cicadomorphab Syrphidsc Coleopterad
55 27 76
68 43 109
72 37 114
– 15 80
35 25 61
22 22 52
33 29 52
– 22 62
133 59 228
0 4 4
Ground invertebrates Coleoptera (excluding carabids)e Carabidsf
36 30
54 21
52 29
25 16
30 18
29 23
35 17
19 18
116 53
1 1
Deadwood invertebratesg
23
24
21
8
20
14
23
2
64
3
Fungi Lichens Bryophytes Vascular plants Songbirds
94 11 25 28 18
249 29 35 34 25
170 14 32 47 27
181 51 37 55 –
210 100 31 27 17
88 23 39 29 16
232 46 54 40 15
127 102 60 60 –
677 202 111 143 40
29 2 0 0 0
494
772
701
534
627
423
623
503
2051
46
Totals
a Beetles – 37 families; b cicalids – 5 families; c hoverflies; d beetles – 30 families; e beetles – 26 families; f ground beetles. g The deadwood invertebrates category comprises data from a number of insect groups, many of which remain to be analysed. It is anticipated that more species will emerge from the deadwood collected from the oak stands. – no data available.
planted forests (Humphrey et al., 1998). A scattering of Red Data list species were recorded
Ground vegetation
across the majority of species groups, but the most
Although ground vegetation diversity was closely
striking result was for the fungi where 29 Red Data
related to soil nutrient levels there was also an effect
list species were recorded, suggesting that
of stand age on vegetation community composition,
plantations provide a particularly valuable habitat for
with the vegetation in most crop types becoming
rare fungi. Fungi, however, have been under-
progressively more wooded in character through the
recorded in the past compared to other groups,
stand cycle (increase in woodland similarity
particularly in plantations, so many of these species
coefficient – Table 2). This process is a function of
may be less rare than previously thought.
stand age (enough time has elapsed to allow slowcolonising woodland plants to become established in the stand), but may also be related to site history, i.e. whether the stand was established on a site previously occupied by ancient semi-natural woodland. Nevertheless, the plantation coefficients are still lower than those of the semi-natural woodland ‘control’ plots (oak and overmature foothills Scots pine), and only time will tell whether the wooded character of the vegetation of the overmature planted stands will continue to develop.
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Table 2 Changes in the woodland vegetation similarity coefficient in relation to stand stage and crop type. The woodland vegetation similarity coefficient gives a measure of how closely the sampled vegetation is matched to a National Vegetation Classification (NVC; Rodwell, 1991) semi-natural woodland community type relative to a nonwoodland vegetation community. Woodland vegetation similarity coefficient (%)
Pre-thicket
Mid-rotation
Mature
Overmature
Lowland Corsican pine
43.2
32.8
27.4
58.2
Lowland Scots pine
21.9
34.6
34.9
32
Foothills Scots pine
41.3
58.2
69.1
70.8
Lowland Norway spruce
56.6
41.9
51
–
Foothills Sitka spruce
33.3
17.5
25.5
36.8
Upland Sitka spruce
44.7
33.9
49.9
58.6
Lowland oak
–
88.9
60.7
–
Upland oak
–
75.4
79.2
–
– Stand stage not available.
Invertebrates
Canopy Coleoptera (beetles) were categorised into
Carabid (ground beetle) species-richness and
predators and others. The main influences on
community composition were strongly influenced by
community composition were tree species and
latitude and canopy structure, and to a lesser extent
latitude. Saproxylic species showed an increase in
by soil organic matter and vegetation diversity.
abundance with plantation age, but no relationship
Species diversity was greatest in the more open
with fallen deadwood volume was found, possibly
plots, either pre-thicket or overmature, declining
due to the narrow sampling window (only one
with canopy closure. There was a significant
sample per year for 2 years in each plot). Predators
increase in the proportion of forest specialist species
were the most abundant group in many plots,
as the stands matured, with the overmature stands
particularly spruce, where the predators associated
having the highest values (Figure 2).
with the green spruce aphid, Elatobium abietinum,
the functional groups saproxyles, herbivores,
were dominant. Higher structural diversity in Scots
% of total carabid species
pine stands resulted in a more diverse canopy 50
Coleoptera community, though this relationship was
40
not found in other tree species. A positive
30
relationship between leaf area index and herbivore
20
species richness in pine suggests that as stands are
10
thinned, the loss of canopy cover has a direct effect on the species-richness of canopy Coleoptera.
0 pre-thicket
mid-rotation
mature
overmature
Large numbers of invertebrates, mainly Diptera
Chronosequence specialists
F I G U R E
generalists
others
2
The increasing proportion of carabid forest specialists with plantation age, together with a corresponding decline in non-forest species.
(flies) and parasitic Hymenoptera (wasps) were collected from the malaise traps. Hoverflies (Syrphidae), tree hoppers (Cicadomorpha) and beetles (Coleoptera) were identified to species level. Analysis of these data is still in progress, but the key points which have emerged are:
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• Hopper and hoverfly species-richness and diversity
counts relating to denser canopy cover. This finding contrasts with those of other studies which have
decreases as mean tree basal area increases.
suggested that the fungal flora of conifer stands is • Beetle diversity is not related to mean basal area. • Pre-thicket plots have the highest hopper and
often less diverse than that of broadleaved stands (Villeneuve et al., 1989). It is possible that the denser stand conditions associated with spruce are
hoverfly diversity.
conducive to the development of mycorrhizal • Sitka spruce canopies support the lowest
communities by affording freedom from competing
diversity for all three insect groups.
ground vegetation and providing a higher tree root density for mycorrhizal associations.
Fungi
In the lowland plots, mycorrhizal species-richness was positively correlated with the number of
The fungi were broken down into four functional
potential host tree species (P < 0.05). This confirms
groups: mycorrhizals, parasites, litter saprotrophs
recent analyses indicating that many tree species in
and wood saprotrophs. The results shown in Figure
Britain are associated with distinctive
3a are for mycorrhizals (223 species in total) and
ectomycorrhizal fungi which, in some cases, may be
wood saprotrophs (180 species). Upland Sitka
host-specific (Newton and Haigh, 1998). Wood
spruce plots had the highest mycorrhizal species
saprotroph richness was strongly correlated (P < 0.05) with increases in fallen deadwood (log)
(a)
volume (Figure 3b), with the lowland Scots pine and Wood saprotrophs
Mean species count (no. ha-1)
35
oak plots having the highest species numbers and
Mycorrhizas
30
log volumes.
25 20 15
Bryophytes and lichens
10 5 0
There was little distinction between the bryophyte d an
la
w
pl
U
Lo
la
K
K
P
O
C
SS
S
N
O
nd
nd
nd
SP
SP
SS
lls hi
la
ot
w
Lo
Fo
w
Lo
d an
nd
lls hi
la
ot
w
pl
U
Lo
Fo
flora of planted stands and semi-natural woodland
(b)
(Table 1). Bryophyte species-richness was more closely related to crop type than climate, with
80
Species count (no.ha-1)
spruce stands being richer than pine stands, regardless of climate zone. This observation has not
60
previously been recorded in Britain, but is consistent 40
with Fennoscandian literature, where spruce is generally considered a more favourable habitat for
20
bryophytes than pine (Esseen et al., 1997). Bryophytes were less affected by shading, and most
0 0
10
20
30
Volume (m3 ha-1)
F I G U R E
3
spruce stands had a reasonable complement of species in all stand stages. The best stands appear to be those with high values for upper canopy cover
(a) Mycorrhizal and wood saprotroph species-richness in relation to crop type. SP: Scots pine, SS: Sitka spruce, NS: Norway spruce, CP: Corsican pine, OK: oak.
(i.e. mature and overmature stand stages). It is
(b) Relationship between wood saprotroph species counts and volume of fallen deadwood (lowland sites only).
and constancy of micro-climate.
possible that these stands offer a better combination of high humidity, adequate light levels
30
upland and foothills stands than in the lowland stands (Table 1), substantiating existing views that oceanic conditions (and low pollution levels) in the north and west of Britain provide much better conditions for lichen growth (Rose, 1993). The seminatural pinewood and oak stands had richer lichen communities than the planted stands, relating to the
Mean species count (no. ha-1)
Lichen species-richness was much higher in the 60 50 40 30 20 10 0 pre-thicket
mid-rotation
occurrence of habitat features such as old trees,
mature
overmature
oak
Stand stage / crop type
shaded rocks and cliffs, and a long-continuity of
Uplands / foothills
Lowlands
woodland conditions (Plate 1). F I G U R E
4
Lichen species-richness in relation to stand stage; oak is included for comparative purposes.
B
P L A T E
1
Ancient semi-natural Scots pine wood showing old trees and standing deadwood. (Simon Davey)
P L A T E
2
Typical group of pinewood lichens including Cladonia botrytes (B) on deadwood; Vaccinium berry added for scale. (Simon Davey)
Low light levels are considered to be highly detrimental to lichen growth (Rose, 1993). This
(Kruys et al., 1999) tend to support these findings.
explains why stand structure had such a significant
Larger and more highly decayed material appears to
effect on lichen species-richness, mid-rotation and
provide a better substrate for lower plant
mature stages having lower species counts than the
development (Ferris and Humphrey, in press).
pre-thicket and overmature stands (Figure 4). The
Snags in native pinewoods provide a key habitat for
pre-thicket stands are particularly important in the
the rare ‘pin-head’ lichen group (species of the
foothills Scots pine plots where stumps support
genera Calicales and Chaenotheca).
Cladonia species. A scarce and important species within the group is C. botrytes shown in Plate 2. Bryophyte species-richness was higher on logs and stumps, while snags were more important for lichens (Figure 5). Observations from overseas
31
Mean number of species
3 2.5 2 1.5 1 0.5 0 logs
snags
stumps
Deadwood type
Bryophytes
Lichens
P L A T E F I G U R E
5
Lichen and bryophyte species-richness on different types of deadwood.
3
Deadwood is an important substrate for lower plants and fungi especially within natural reserves. (Simon Davey)
1. Maintenance of the patch-clearfelling system to
Conclusions and implications for management
ensure provision of early-successional habitat. 2. Extending rotations beyond normal economic felling age and establishing ‘natural’ (non-
The project has been successful in meeting its main objective of establishing a baseline dataset of the biodiversity of plantations across Britain. The most significant finding was that stands of non-native conifer species appear to provide suitable habitat for a wide range of native flora and fauna and should be viewed as making a positive contribution to
intervention) reserves. 3. Managing some stands under continuous cover regimes (sensu Mason et al., 1999). The latter two strategies would help to maintain and develop mature woodland conditions, including production of old trees, accumulation of deadwood (Plate 3) and diversification of the tree flora.
biodiversity conservation in the UK. There were considerable differences in value of different stand
While wind risk is a significant factor to consider
ages and crop types for different species groups
when deciding where to locate continuous cover
with no single type providing ‘optimal’ conditions for
stands (Mason et al., 1999), site history is also of
biodiversity. Pre-thicket plots and restocks provide
key importance, as there is a suggestion from the
habitat for a variety of species-groups common to
data that plantations established on ancient semi-
non-wooded habitats (e.g. heathland). However, the
natural woodland sites (PAWS, e.g. some lowland
overmature stands, both in native and planted
Norway spruce and upland Sitka spruce stands) have
forests, are important for species requiring
a much higher diversity of woodland fungi,
continuity of wooded conditions and deadwood.
bryophytes and vascular plants than their counter-
Therefore, three contrasting, but not mutually
parts established on previously open ground.
exclusive, management strategies could be
Restoring PAWS back to native woodland may not
considered for plantations:
always be of benefit to biodiversity in the short to medium term, particularly if the restoration is done
32
very rapidly. This is especially the case for
mycorrhizal diversity. The positive correlations
mycorrhizals where extensive felling of host trees
recorded between deadwood volumes, and species-
can disrupt mycelial connectivity and reduce the
richness of wood saprotroph fungi, lichens and
extent of recolonisation after restocking or natural
bryophytes is also notable. A mix of fresh and well-
regeneration (Flynn et al., 1998). Even smaller-scale
decayed large diameter logs and stumps should
felling can be disruptive (Flynn et al., 1998), and it
provide a range of habitat types (Plate 4) with
may be more desirable therefore to identify some
volumes in the range of about 40 m3 ha-1 providing
PAWS known to have a high number of
for the greatest lower plant and fungal diversity
characteristic species as potential ‘natural reserves’.
(Ferris and Humphrey, in press). The biodiversity indicators and management strategies proposed in this article are still tentative and further work is planned in the near future to validate these proposals and analyse additional datasets, looking particularly at the issue of site history.
Acknowledgements
The following individuals and organisations made a significant contribution to this research: Andrew Brunt, Ellie Dickson, Becky Lander, Su Meekins, P L A T E
4
Old beech stump. Fresh and well-decayed large logs and stumps provide a range of habitat types. (Entomology Branch, Forest Research)
Antonia Nichol, Martin Schofield, Lorna Parker, Robin Sturdy, Phil Ratcliffe, Bill Mason, Graham Pyatt, Simon Hodge, Clive Carter, Derrick Hiscocks, Simon Davey, the Technical Support Unit of Forest Research, the British Mycological Society, the British
Based on the results presented above it is clear that measures of stand structure and deadwood have considerable potential as biodiversity indicators in planted forests. For example, the number of host tree species could be used as an indicator of
Trust for Ornithology, Forest Enterprise, Crown Estates, Highlands and Islands Enterprise, Alvie Estates. The research was funded by the Forestry Commission.
33
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